Flat panel displays are intensively used as information display devices such as mobile phones, personal digital assistances (PDAs), personal computers and televisions.
As far as the mobile phones and the personal digital assistances are concerned, for example, the flat panel displays provide advantages that: they enable necessary information to be obtained wherever the information is desired; and the like. However, in some places, an image displayed on the mobile phones or the personal digital assistances is highly likely to be subjected to peeking by person(s) around a user, which causes an issue of privacy such as leakage of personal information.
In addition, some flat panel displays include a touchscreen in order to improve ease of operation for users, speedy operability, and the like. Such flat panel displays that include the touchscreen are employed in ATMs (automated teller machines) installed in banks, for example; however, if a security code or personal information is subjected to peeking by person(s) around a user when the user inputs the security code or personal information through the touchscreen, such information may be used for improper purposes.
In view of such problems, in these days, a view angle-restricting sheet has been proposed that can prevent peeking by person(s) around a user by restricting a view angle (see Japanese Unexamined Patent Application, Publication No. 2010-223996).
The view angle-restricting sheet (which may be referred to as “view angle-controlling optical sheet”) includes a first region that yields a narrow view angle on a display screen, and a second region that yields a wide view angle on the display screen. The view angle-controlling optical sheet is characterized in that the first region is formed by alternately arranging: light transmission sections that contain an optically transparent material; and light-absorbing sections that contain a light-absorbing material. The view angle-controlling optical sheet can extract rays of light having an incident angle falling within a certain range of angle, predominantly including those perpendicularly oriented, and absorb rays of light obliquely oriented on the light-absorbing section, and therefore the peeking by the person(s) around the user from the oblique direction can be prevented. However, in the view angle-controlling optical sheet, the light-absorbing sections are arranged at a constant interval, and therefore the view angle-controlling optical sheet has a disadvantage that a reduction in front face luminance is likely to be caused.